The present invention relates to a device for measuring the bending strength of sheet material such as corrugated fiberboard or paperboard, at a creased, scored, or blank portion thereof.
Typically, to manufacture containers, suitable sheet material can be subjected to a printing process and cut into a desired shape by means of a die board. The die board can also make slits, scores or creases, which aid in the formation of a container by reducing the force necessary to bend the sheet into a desired configuration. Typically, the creased portions of a sheet material can be guide lines for folding the sheet material and creating flaps from portions of the sheet material, which can then be configured or folded to make a box or other type of container.
Regarding the various means of creasing or scoring the sheet material, the warping force of the creased portion varies with the methods selected for making the crease. For example, when a crease is prepared as a series of holes by means of a laser beam, the warping force of the creased portion varies with the differences in size of each hole and with the differences in spacing between adjacent holes. The warping force of the creased portion also varies with the clearance between the edge portion of the sheet and the portion to be folded or creased. In addition, the warping force of the creased portion also varies with the materials used in the corrugated fiberboard and with the conditions of the formed crease.
As a consequence of the aforementioned variations in the warping force of the creased portion, the following problems can occur. In a case where the boxes are used for packing a wide variety of products on packing lines under automatic control, the step of fixing the top and bottom flaps of each box together by adhesive tape is performed as a last step in the packing process. The height of the empty box depends on the warping force of the creased portion, the box's own weight, and the symmetry or proportion of the box's shape or dimensions. When the warping force of the creased portion is too high, each flap of the corrugated box tends to extend higher than the acceptable height or width of the box with respect to the packing line. If the flaps of the corrugated box extend too high, it is difficult to place the box correctly on the line and to prevent it from becoming entangled with equipment along the line, which may cause the packing line to be stopped.
Recently, automatic high-speed packaging apparatuses have been introduced in the food and drink industries, and containers made of paperboard or corrugated fiberboard used in those fields can suffer serious damage depending on the quality of the creases formed thereon. Accordingly, manufacturers of paper containers and corrugated fiberboard have tried to develop a quality control method with a particular emphasis on the strength of the crease.
The strength of any portion of the sheet material, except the creased portion, is directly related to the strength of the resulting container. It is therefore important to understand the bending strength of the sheet material independent of the bending strength of the creased portions of the sheet material, so that the relationship between the two can be established for each type of sheet material, and from the point of quality control.